Heat stabilized cellulose yarn



Patented Sept. 22, 1955 HEAT STABILIZED CELLULOSE YARN William EarlRoseveare, Richmond, Va., assignpr to E. I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing.Application October 1947,, Serial No. 779,208

3 Claims. (Cl. 11771) 1 This invention relates to organic textilestructures such as yarns, threads, cords and the like, and moreparticularly, it relates to the treatment thereof with a material forincreasing the resistance of such organic textile structures todeterioration by heat.

Certain cellulosic yarns, for example, regenerated cellulose yarns, havethe disadvantageous characteristic of deteriorating to a considerableextent when subjected to elevated temperatures. While certain materials,such as urea or biuret or phenyl biguanide, have been used successfullyas heat aging inhibitors, more effective agents have been desired toreduce even further the extent of deterioration in the yarns.

It is an object of the: present invention to treat cellulosic and otherstructures in such a manner as to increase their resistance todeteriorationv by heat.

It is another object of this invention to treat certain structures, forexample, regenerated cel-' lulose yarns having high dry tenacities, insuch a manner that the resultant yarns will have: an increasedresistance to deterioration by heat..

It is a further object of this invention to prepare articles containing.cellulosic or other yarns, as, for example, regenerated cellulose:yarns, which articles are' suitable for' use at elevated temperatures.

Astill more specific object of the present invention is the productionof. rubber goods reinforced with cellulose yarns, for example,regenerated cellulose yarns which have been treatedin such a manner asto increase their resistance by heat.

Other objects of the invention will appear hereinafter.

The objects of the invention. may be accomplished, in general, byintimately associating the structures, for example, regeneratedcelluloseyarns, with a readily oxid-izable metal. For purposes of thisinvention such a metal. isone Whichat temperatures of about 150 Ctreactswithboth air and water to form alkaline" products. products are inthemselves heat-aging inhibitors. The metals preferred for use in the:process of. this invention are those which have. only one positivevalence and those whose hydroxidesare no more water-solublethan'strontium: hydroxide. It has been discovered. that both: moistureand oxygen hasten heat degradation and that. when they are actingsimultaneously a synergistic effect'results- This invention; then, isbased upon the removal of botlr water and oxygen by reaction with: ametal; Advantageously, in the removal These of degradative materials, asoxygen and water, by the process of this invention, increased usefullife of the structure results. The desired application is conducted sothat the resultant structure contains an optimum amount of theparticular metal being used. Other factors being equal, the degree ofincreased resistance to deterioration by heat of the structures thustreated will be proportional to the amount of metal with which they areimpregnated, up to a certain limit.

In accordance with the present invention, it has been discovered thatcellulosic and other structures, for example, regenerated cellulosethreads such as viscose rayon threads, or cuprammonium rayon threads,may be stabilized against the deteriorative action of heat by impregnation of the threads with ametal such as aluminum or magnesium.Whereas an untreated regenerated cellulose thread subjected to heat ingat C-. for a period of 4 hours in sealed tubes containing air and I2%moisture shows a loss of strength of over 50%, similar yarn whenimpregnated with about 0 .2 of magnesium flake shows on heating for 4hours at 150 C. a loss of metalby' the process of this invention. Theseexamples, wherein parts are by weight, are illustrative only and are notto be construed as limitative;

Example I A. high tenacity regenerated cellulose yarn produced by theviscose process was passed through a slurry consisting. of magnesiumflake suspended in an 8% aqueous solution of polyvinyl alcohol (a 4%aqueous solution of this polymer at 20 C. has a medium viscosityo'f 24centipoises). The suspension was maintained by stirring; After the cordwas run through the slurry, it was partially dried and was then dippedinto a bath containing an adhesive. The adhesive was aresorcinol-formald'ehyde-rubber latex adhesive which was predominantlyrubber latex. The yarn was then dried by hot air at a temperature of 105C. The speed of yarn travel during these operations was about 5 yardsper minute. The quantity of magnesium deposited on the yarn was about0.3%. The heat aging was conducted in all cases in sealed tubes heatedto a temperature of 150 C. and maintained at that temperature for 16hours. These conditions were employed to simulate the conditionsobtaining when the structures are covered with relatively impermeablecoatings which prevent the free escape of degradation products.

The cords treated with magnesium and then dipped in the adhesive bathand dried st only 14.2% of their original strength whereas dipped,untreated cords run as controls lost over 23% of their strength. Aspointed out in copending application, Serial No. 717,813, new U. S.Patent No. 2,577,593, similar yarn protected with 0.22%l-phenylbiguanide lost 16% of its original strength after 16 hours at150 C. and yarn protected with 0.25% urea and similarly heat-aged lost62% of its strength. Thus, it is shown that the process of thisinvention is an effective means of stabilizing cellulosic yarns againstthe deteriorative action of heat.

Example II Several samples of cotton tire cord were heated L at 150 C.for 17 hours in sealed tubes containing air and about 6% moisture. Afterthis treatment the cords possessed, on the average, only 32% of theiroriginal strengths. A similar set of samples was impregnated with anamount of magnesium powder equal to 1% of the weight of the cotton.These impregnated samples were similarly aged. The impregnated cordswere found to have, on average, 47% of their original strengths. Uponcomparison of the above figures, the inhibiting effect of magnesium canreadily be seen. Like cotton structures those composed of polyarnides,such as polyhexamethylene adipamide, polyhexamethylene sebaceamide andthe like, or polymeric esters, such as those prepared from terephthalicacid, are stabilized against degradation by heat by impregnation withmagnesium as described above. Any of the metals of this invention may beused with structures composed of these non-cellulosic polymers to obtaingreater heat stability.

Example III Several samples or nylon tire cord were heated at 150 C. for16 hours in sealed tubes containing air and 3.4% moisture. After thistreatment, the cords possessed on the average only 40% of their originalstrength. A similar set of samples was impregnated with an amount ormagnesium powder equal to 1% of the weight of the nylon. These sampleswere similarly aged. The impregnated samples were found to have lostappreciably less than 25% of their original strength.

Example I V Skeins of yarn taken from one spool of bobbinspun, hightenacity, regenerated cellulose yarn used commercially in preparingtires were treated in the following manner: Six of the skeins weredipped in a finish comprising about 1.5% of the composition Z describedbelow, about 0.5% polyvinyl alcohol and 98% water. The composition Zconsisted of about 25 parts of sulfated peanut oil, 25 parts of asulfated fatty acid ester such as the sulfated glyceride of oleic acidor other higher fatty acids, 17 parts of mineral oil, 17 parts of peanutoil and 17 parts of a fatty acid ester. These six skeins were not heataged. Strengths, that is dry tenacities, were measured on these directlyto obtain a representative figure for comparison to heat-aged yarns.Four skeins, referred to as lot A in the table below, were similarlydipped and then aged. An additional six skeins were treated by runningthe yarn through a bath containing in addition to the above finish 0.5%of aluminum flake. These aluminum containing skeins were dried at 60 C.and allowed to condition in the standard testing laboratory atmosphere.Two of the aluminum containing skeins were not heat aged (lot B) and ofthe aluminum containing skeins were heat aged (lot C).

Percent Strength Losses Finished, heat aged controls Aluminumimpregnated, imaged Aluminum impregnated, heat-aged Magnesiumimpregnated, unaged Magnesium impregnated, heat-aged By comparison ofthe above figures it can be seen that in these experiments the magnesiumcontaining yarns have the lowest strength losses on heat-aging. Furtherimprovement in the use of magnesium for increasin the resistance ofcellulosic yarns to deterioration of heat may be obtained by usingmagnesium flake of very small mesh. The magnesium flake used in theabove experiment was mesh whereas the aluminum used was in the form of afine powder. It is dimcult to obtain a proper dispersion of themagnesium in the finish when such large particles are used. Further, itcan be seen that a loss in strength of 3.7% occurs merely inimpregnating with magnesium whereas no loss occurs in impregnating withaluminum. It is believed that the 3.7% loss is due to abrasion of theyarn caused by the large particles of magnesium. For example, betterresults may be obtained by the use of magnesium in fine flake form.Further, the finer the particle size the more intimate is the contact ofthe inhibitors with air and moisture. Thus, for best results it ispreferred to use the metals in finely divided form. Of course, themetals incorporated, will be substantially unoxidized. The magnesium,after heat-aging, looks like an ash, the magnesium particles havingreacted with moisture and air to form magnesium oxide or magnesiumhydroxide or magnesium carbonates. Such alkaline materials act furtheras inhibitors for heat aging, since they neutralize any acidic compoundspresent.

Similar alkaline products are formed when aluminum is used. However,aluminum does not appear to be changed as extensively as magnesium. Thisis to be expected since magnesium is the more reactive metal. Any commonmetal which becomes oxidized with comparative case at elevatedtemperatures, for example, about C., and which reacts with water orsteam may be employed providing it or its reaction products will notreact with the physical structure 'to -deteriorate it. Thus, metal otherthan 'magnesium and aluminum may be employed, "such as strontium orcalcium. It is preferred *to use those metals whose hydroxides are notmore water-soluble than strontium hydroxide. The reactiveness or alkalimetals 'and barium andthe alkalinity of their hydroxides lirriits theirusefulnes in this invention. Certain "other *metals, such as zin'c,cadmium, lead andtin, c'an 'form peroxides which tend to'degrad'ecertain structures, as, for example, those of cellulose.Accordingly, it is preferred fto use those metals which do not have avariable-valence'andwhich do not form peroxides. ot-those :metals whichhave-only one valence,'-it is preferred-tofuse-ma nesium or-alu'minum,"thi'sjprefereiic'ebeing based upon their chemical reactivity, upontheir availability and upon the inertn'ess of 'the-metaIstheir oxidesand salts' toward' cellulose.

One method of application'consists of simply immersing thestruc'ture inaproper-"medium containing the metal suspended therein in properconcentration. "The medium-may also contain-a finish. The application offini'sh is'not necessary to the heat aging inhibition effect, as shownabove in Example "I, but is preferred because inter-filament lubricationis obtained which facilitates the-obtainingof proper twisting and thedesired mobility of the filaments '=in the final structures. Incommercial operation the -'metal may be appliedeitheriinmediatelyprevious 'to or in conjunction with -'the application of arubber .adhesive in thepreparation of-useful rubber articles. Thus, itis not necessary to employ an extra size or finish. The rubber adhesivebeing used in the particular commercial'operation may act as a vehiclefor the metal fiake such as the magnesium flake. 'The treatment of the'cellulosic threads withare'sin late'x 'adh'e'si've may be in the manner*of Charch -'and Maney, 3. 2,128,635 and the types of adhesives fdisclosed therein or an other adhesive '-treatmeiit =may be employed inthi's invention. While theproces'sof this invention is applicable touncoated structures, it is used chiefiy in -the preparation of coatedstructures. Elie coatings ma'y be -'prepared from any ofthefcommercially available polymers. It is --preferred to use a coatinghaving a lowperm'eability to' air and moisture. For the most part,such-coatings reduce the- -amount of air and moisture difiusing into theyarn' to an amount less than that which may be taken up by theinhibitors. 'Aspoint'ed out above, the process of this invention isparticularly useful in the preparation oi rubber articles, employingeither natural or synthetic rubbers. Other polymers which maybe used,amonga largenumber, are vinylpolymers a polyvinyl chloride, polyvinylacetate, polyvinyl butyral, polyethylene interp'olymers of vinylchloride-vinyl "acetate, vinyl chloride-vinyl cyanide,hydrolyzed'ethylene-vinyl acetate interpolymers, vinylidenechlorideinterpolymers, rubber hydrochloride, chlorinated rubber, etc.

In'i-mmersion processes, the-structure, such as a yarn, in a form of asingle-- strand ora-"fabric,

may be passed continuouslythrough the bath so that a suitable length ofthe structure is immersed at any instance and so that it runs at asuitable rate or the immersion may be accomplished by simply dipping anentire structure, for example, a skein, in the solution and allowing itto remain there for a suitable period of time. If

the impregnation is by passage of a sin n of yarn through a 'bath, it isimportant .that this be done without the application of undue -tensionto the yarn or with as little tension as is practioable in order toattain the penetration of :and hence the greatest stabilizing activityfrom a given amount of metal. 'Thisis accomplished by running the yarnover 'asimp'le system :of freely rotating pulleyseoas to-give a lengthof yarn of about 30 inches immersed at any instant and being wound up ona mechanically driven areel. The reel :is rotated'at suchazspeed thatthe rate of traverse of the yarn through the bath is about yards perminute and the period of immersion Iis, :therefore, about 40.5 seconds.(Dther yarn speeds ranging from 10 to 300 yards per minute may also beused. After passage through the bath, the :yarn is Iallowed to :remainon "the reel until dry. :Drying may also -Joe accomplished using ovens,contact driers or air drying means. The temperatures for "drying :mayvary from about 70 C. to about- C.

If the impregnation is by .dipping 'the structure, such :as a skein or.yarn,.in a bath allat once, the structure may lbeffreed .of excessiveliquor by wringing out in:a:centrifuge or. by other suitable means.-When bathlme'diumsareused, they may be unheated .or heated as desired.Methods other than immersiontproeesses may be employed. For example, the.metal :may he melted in an are or atflameeand then blown as a finespray :onto ith'e structure many of the well known methods of applyingmetals to textiles. In any of the .methods,.itiis Ipreferred itO applythemetal to theifinish'ed structure to iavoidilo'sses whichoccurinrtwistingoperations. For-example, lit-has beentshownthatisuchilosses oiimetal ocour when the i. metal is 5. applied :to-.yarn which is rthen'twisted. The-loss of metal which occurs depends,among other factors, .upon' the degree of subdivision or'the metalusedz'andaupon the nature of thefinish, sizeor adhesive employed.Further, in any ofithe methods,ithe'concenrtration of the Imetal inith'e bath or in the spray' is'determined by the extent towhihittisdesiredto impregnate theyarn or-cord. 'Itis apparent that onemay stabilizeithe'iyarn' rtothe desireddegree by varying the amount :ofmetal applied to theyarn or the extentof the impregnation. Efiectiveresults are :obtained using :concentrations of magnesium from :*about0.2 to about 2-.0% "by weight of the yarn :or cord. For :reasons ofpracticality and :economy, the preferred concentration is from about 0.5toabout 1.5%. "Similar concentrations of :aluminum flake or other metalsmay be used.

Although it will :generally be desired to treat the structures accordingi to' the immersion method described above, "other bath' ingredients maybe used than those mentioned. Instead: of water as a vehicle, organicliquids "or mixtures of thesewith or without water may 'be' employed.For example, cyelo'hexa'ne, benzene, and-similar liquids maybe employedin the-immersion'baths providing these liquids permitthe formation ofthe desired dispersion of metal. Likewise, it-is possible to use theadhesive as a dispersing medium. *Other liquids may be-a'dded totheadhesive to give the desired fluidity. The adhesive, which is used toobtain more stable impregnations, is not essential and may be dispensedwith, as, for example, in the spraying methods of impregnation. In thesemethods or other methods it is possible to spray the adhesive on alongwith, prior to or after the application of the metal,

Finishes other than composition Z mentioned above may be employed andsizing agents other than polyvinyl alcohol may be used. In general, anyof the numerous, well-known cellulose finishes and sizes may be employedin the baths to obtain better adhesion of the metal to the structuralmaterial, such as cellulose, providing, of course, the compositions arenot reactive toward the agents of this invention. Dispersing agents mayalso be incorporated in the baths to obtain stable dispersions of themetal. The particular dispersing agent may be chosen from the multitudeof well-known dispersants taking into consideration the nature of thesize, finish or adhesive in admixture with which the metal is to beapplied. While finishes, sizes and peptizing agents are not essential tothe process of this invention, they may be used frequently to obtainbetter uniformity of impregnation and greater adhesion. Generally, it ispreferred to use a bath containing about 1.25 to about 1.75% of afinish, about 0.4 to about 0.6% of a size such as polyvinyl alcohol andabout 0.4 to about 0.6% of magnesium flake. A bath of this compositionwhen used in the process of this invention will lead to the impregnationof the structure to an extent which efiectively protects it for aconsiderable length of time at high temperatures without loading itexcessively.

Furthermore, the process of this invention may be applied to theimpregnation of thread such as viscose rayon yarn while it is still inthe gel state.

The increased resistance to deterioration by heat imparted by theprocesses of this invention to the structures of this invention, such ascellulosic yarn or cord, makes the yarn particularly useful where it isto be subjected to elevated temperatures. Viscose rayon yarn or similarcellulosic yarns so treated to associate the metal intimately with theyarn, may be used for all purposes to which such a yarn might otherwisebe put and which subject it eventually to elevated temperatures such aswould more rapidly destroy the usefulness of the untreated than thetreated yarn. The yarn treated according to this invention may betwisted into cord or other materials for use as reinforcement for rubberarticles, including motor vehicle tires and steam hose. Such treatedyarn will Withstand, far better than the untreated yarn, deteriorationduring the manufacture of rubber products involving such operations asvulcanization at elevated temperatures or in use where the products aresubjected to elevated temperatures. Also, yarn so treated may in oneform or another be Woven into fabricsfor uses at elevated temperatures,as for example, coverings for laundry mangles and as zinc oxide fumebags.

Among other uses for treated structures of this invention are automobiletop materials; masks and protectors around steel furnaces and the like;fabric tubes for discharge ends of chutes for hot materials as in cementmills; bags for heating pads; strainers for hot oil and other nonaqueousmaterials; belt driers such as on blueprint machines; and conveyor beltsfor hot materials. In general, this invention may be ap- 8 plied to themanufacture of coated fabrics or similar articles which are exposed toelevated temperatures.

Whereas present cellulosic yarn, such as viscose rayon yarn, isordinarily deteriorated on exposure to heat, the present invention makespossible the treatment of this yarn so that it possesses a markedstability under the same conditions. This is true also for structurescomposed of cellulose derivatives, of polyamides or polymeric esters.The use of metal such as aluminum and magnesium has the furtheradvantage in that impregnation of organic textile struc tures will causevery little loss of the initial strength of the structures. The use ofthese metals is furthermore advantageous in that the protective chemicalreactions they induce do not occur extensively at low or roomtemperatures. That is, the metals are retained for use at the hightemperatures at which they are needed, no loss of metal or protectiveaction occurring because at consumption of the protecting agent at lowertemperatures. Even if the metal is converted to some extent at lowtemperatures, to its oxide or a salt, such as its carbonate, no loss issustained since these alkaline products are effective heat ageinhibitors. The metal, heat-aging inhibitors of this invention arefurther advantageous in that they are relatively inexpensive materialsand very readily obtainable.

Since it is obvious that many changes and modifications may be made inthe above described details without departing from th nature and spiritof the invention, it is understood that this invention is not limitedexcept as set forth in the appended claims.

I claim:

1. A heat stabilized article comprising a yarn produced from regeneratedcellulose impregnated with about 0.2% to about 2.0% of fine particles ofa metal selected from the group consisting of aluminum and magnesium,said impregnated yarn being coated with a rubber.

2. A heat stabilized article comprising a yarn produced from regeneratedcellulose impregnated with about 0.2% to about 2.0% of fine particles ofmagnesium, said impregnated yarn being coated with a synthetic rubber.

3. A heat stabilized article comprising a yarn produced from regeneratedcellulose impregnated with about 0.2% to about 2.0% of fine particles ofmagnesium, said impregnated yarn being coated with a natural rubber.

WILLIAM EARL ROSEVEARE.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,184,015 Price May 23, 1916 1,825,252 Taylor Sept. 29, 19312,034,008 Taylor Mar. 17, 1936 2,227,843 Quenelle Jan. 7, 1941 FOREIGNPATENTS Number Country Date 432,019 Great Britain July 15, 1935

1. A HEAT STABILIZED ARTICLE COMPRISING A YARN PRODUCED FROM REGENERATEDCELLULOSE IMPREGNATED WITH ABOUT 0.2% TO ABOUT 2.0% OF FINE PARTICLES OFA METAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM AND MAGNESTIUM,SAID IMPREGNATED YARN BEING COATED WITH A RUBBER.